Method of treating an ore material



Sept. 28, 1937.

. T. A. MITCHELL METHOD OF TREATING AN ORE MATERIAL Filed No v. 5, 1934 2 Sheets-Sheet 1 3 5 o 9 a 1 1 a 5 4 .6 a WL A l 6 L 4 E 4 T a 2 i a w H Q h I 4.5: //////////A/ W xv i a 4 a I o 4 w I\\ 4 2 1. M 5 J m a 4 M a m e T I 3 Q \u 7? a a c 2 v 7 "i M I w 0 m M. 1 w l C m R O o H Sept. 28, 1937.

Filed Nov. 5, 193

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T. A. MITCHELL METHOD OF TREATING AN ORE MATERIAL I Cmommzsa ORE gwue /Mioo THo/ ms Iq-MITCHELL ..2 sheets snee 2 Patented Sept. 28, i 1937 METHOD OF TREATING AN ORE MATERIAL Thomas A. Mitchell, Denver, (3010., assignor to Hughes-Mitchell Processes, Incorporated, Denver, 0010., a corporation of Wyoming Application November 5, i934, Serial'No. 751,477

8 Claims.

This invention relates to a method of and an apparatus for solubilizing ore metal values, and particularly for treating ore metal sulfides by a series of steps involving a roasting operation to remove sulfide sulfur therefrom, and a subsequent treatment to recover the desired metal as a soluble salt.

Various types of ore treatments require wetting the ore material prior to a roasting operation; 10 and one object of this invention is to provide a simple, economical and eflicient method of drying the ore material prior to its being roasted.

Further objects are to coordinate the drying and roasting operations in such a manner that each is beneficial to the other, and particularly in the utilization of the waste heat from the roasting operationior drying the wet ore material, and to provide an efficient apparatus for carrying out the various steps of the two operations.

l A still further object of the invention is to provide an efiicient and economical process for chloridizing an ore material, and particularly a sulfide ore, by a series of steps which cooperate to solubilize substantially all of a desired ore metal value, such as the zinc compounds in a complex ore material. V

Various other objects will be apparent in the following disclosure.

I Referring to the drawings, I have there illustrated, both in a flow diagram and in a diagrammatic showing of apparatus, how a complex sulfide ore may be treated in accordance with the difi-erent phases of this invention. r In these drawings:

Fig. 1 shows diagrammatically a series of apparatus arranged for drying a wet ore material and then roasting it by a flash roasting operation; and g 40 Fig. 2 is a flow diagram showing the principal steps of two alternative procedures for spray drying and roasting an ore and thereafter chloridizing the roasted material.

As indicated in the drawings, this invention may be applied to the roasting of an ore intermixed with an alkaline earth material for the purposes and in accordance with the method set forth in the patent to Mitchell No. 1,943,331 dated January 16, 1934. The invention may also apply to the treatment of an orc which has been'concentrated by a flotation method, whether or not an alkaline earth material is to be intermixed therewith during the roasting operation, as well as to various other ore materials which are tobe roasted after intermixture with water.

in the first case, inwhich an alkaline earth material, such as lime, is employed to aid the. roasting foperation, the .ore and lime in finely divided condition, such as will pass through a screen of meshes to'the linear inch, is sup- 5 plied from two storage bins l0 and II, and then intermixed with a controlled amount of water introduced by ,means of a pipe l2 into the mixing vat 13. The mixture is then conducted to a rotary mixing apparatus M which is suitably 1o rotated by driving mechanism [5, comprising in the present instance suitable gears driven by a pulley. The interior of the mixer may be in accordance with any standard construction, and it preferably has bafiles arranged to lift the mal5 terial and cause its various ingredients to be thoroughly mixed as they fall within the mixing chamber. It is, of course, feasible to employ other mixing apparatus, such as a ball or roller mill which will aid in crushing the ore and lime dur- 20 ing the mixing operation. Many other standard pieces of apparatus are available. The wet mixture is caused to flow through a suitable collecting pipe 16 into the tank I! where it is held in storage for use in the process. It is to'be under- 25 stood that this ore material is in the form of a pulp or sludge which contains suflicient water to insure that the lime is in intimate association with the ore particles and that the material has a proper physical consistency for flowing through 30 the pipes of the system. The amount of water is regulated primarily in accordance with the requirements of the ore material as to its lime content, it being desirable to bring the two into very intimate association so that after the ore 35 material has been dried, each ore particle will carry a coating of lime thereon, and the lime will be in a protective position during the roasting operation and thus aid both in preventing'the formation of an ore metal sulfate, such as zinc sulfate, as well as in keeping the particles physically separated and so preventing their sintering together and forming impenetrable agglomerates.

As illustrated in dotted outline in Fig. 2, an

ore material may be concentrated 'by a flotation 45 process to form a bulk concentrate and avoid the necessity for roasting and chloridizing a large amount of inert gangue. In accordance with this procedure,- the ore is ground and then fed to a flotation machine in which the sulfides are floated off from the gangue and conveyed by water to a Dorr thickener. Ordinarily, the thick pulp as thus obtained would be fed to a filter, and preferably a rotary filter of the Oliver type, to

which air suction is applied to form a partially 55 dried cake. The concentrates in such a cake would carry from 8 to 12% of moisture, and if these concentrates were fed directly to a shelf roaster, the top shelf would necessarily have to become a drying shelf and thus waste a part of the roasting equipment. Moreover, such a product from the Oliver filter could 'not be fed directly to a flash roaster but would have to be dried initially and pulverized before it could be blown into the roaster. In accordance with this invention, the pulp may be taken from the Dorr thickener and be sent directly to the spray drier hereinafter described, and without passing through the intermediate step of filtration. Hence, in accordance with this aspect of the invention, the concentrates in water, after the flotation or other step of separation of the gangue from the sulfides of the ore, are fed directly to the storage tank I! above described or are otherwise introduced into the spray drier. If desired, lime may be mixed with the ore concentrates in accordance with the requirements of the parti- -cular ore being treated, and the various other features of the invention set forth in the abovementioned Mitchell patent may be incorporated in this process, as desired.

In accordance with a primary feature of this invention, the wet ore material, as above de-' scribed, or any other suitable ore pulp, is dried by a spray drier, and the dry particles are then subjected to a flash roasting operation. It is preferable that the waste heat from the flash roaster be employed either directly or indirectly for drying the wet ore, such as by passing the roaster gases into the drying chamber or preferably a gas, such as air, which has been indirectly heated by the roaster gases. In this way. I utilize the heat of combustion of the ore metal sulfides for drying the wet sludge. A suitable apparatus for this purpose is illustrated diagrammatically in Fig. 1 of the drawings, in which the parts are shown out of their true proportions in order to make clear the various steps of the process involved.

The spray drier may comprise any suitable apparatus, such as a standard Peebles drier or other types on the market. It is illustrated diagrammatically as comprising a casing 20 into which the wet ore sludge is fed through the pipes 2| by means of a suitable pump 22. Heated air or other gas is introduced into the drier chamber through the pipes 23 and 24, as supplied thereto by means of a suitable fan 25. The upper hot air pipe 23 opens into an annular chamber formed by the inlet pipe 2| and an outer pipe 26 concentric thereto. A plate 21 suitably supported beneath the outwardly flared end of the pipe 26 serves to cause the hot air to issue laterally into the drying chamber. Likewise, a conical partition 28 in the bottom of the chamber serves to conduct the hot air from the pipe 24 to another annular, radially ex tending passage between the rotating plate 30 and the flared end of the cone 28. The upper side of the plate 30 is shaped as a pan having an upturned flange. This plate is mounted on the shaft 29 suitably supported within hearings in the base of the drier chamber and it is rotated at a high speed by an electric or other type of motor 3|. It will, therefore, be appreciated that when the wet ore material is forced into the casing, it strikes the centrally located rotating plate 3| and is thrown outwardly and upwardly and is thus disintegrated into separated particles, and as these are thrown outwardly they very rapidly.

The dry ore particles, which were preferably crushed initially to a size of 100 meshes or finer, fall to the bottom of the casing and are removed with the air current by means ofthe fan 33. The dry ore material, with the air and steam, then passes into a cyclone or other suitable separator 34 where, the ore particles are separated by centrifugal force from the gases and the air and steam pass upwardly through the exit pipe 35 to the atmosphere. It will be understood that this cyclone separator is of standard type in which the material is introduced tangentially into the cyclone'casing. As the material whirls around the lower end of the pipe 35, the dust; particles are forced toward the casing wall and thus creep down the wall by the aid of gravity, while being separated from the gases, and the latter pass upwardly through the outlet pipe. The drawings illustrate merely diagrammatically the general-principles of one standard form of drier.

The ore material is now dry and ready to be roasted, and for this purpos'e the dry ore particles pass downwardly through the pipe 3'! into a suitable conveyor, such as a screw conveyor 38 suitably rotated by power mechanism, which conveys it to a position for introduction to the flash roaster. A rotary valve 39 rotated by any suitable power mechanism serves to introduce the dried ore material into the flash roaster 40 and at the same time prevent the escape of gases through the valve in either direction. A blower may be employed, if desired, to feed the material into the furnace in a separated, finely divided condition.

The flash roaster 40 may be of suitable construction. It is illustrated diagrammatically as comprising a large closed heat insulated casing of suitable material. A vertical partition 4| may be located therein to aid in separating the ore material from the roaster gases. Air is fed into this roaster casing through a suitable inlet pipe 42 which may be located in any'required position for the purpose. The bottom of the roaster casing is preferably formed in a hopper shape at each side of the partition 4|, so that the roasted ore particles will gravitate into the collecting pipes 43 and 44, from which the particles are removed by means of the fan 45 and pass through the pipe 46 to subsequent stages of the process. A cyclone separator may be incorporated in the outlet pipe 46 to separate roaster gases from the ore material. I

In order to roast the ore material, it is preferable to heat the walls of the roaster chamber initially, as by means of hot gases, and, if necessary, to supply heat during roasting, as by preheating the air. Then, the ore material is fed at a suitably regulated rate through the rotary valve 39 and allowed to-fall freely as separated dust particles through the extensive space .of the chamber. Here they meet a current of hot or cold air introduced in regulated quantity, and the sulfide sulfur of the ore'is burned and thus removed from the ore particles. This serves to form zinc oxide and/or zinc sulfate from the zinc sulfide. Similarly, the iron pyrites is oxidized preferably to ferric oxide for use in subsequent stages of the process. It, however, will be understood that the-roaster operation may be suitably regulated to obtain the ore material in any desired condition, in accordance with Well-known standard practice; andthis invention is not to be construed as limited to any particular method of operation. It is readily understood that by limiting the air supply or by the use of reducing gases in a second stage roaster treatment, a lower oxide of iron may be obtained, if required for the subsequent ore treatment where, for instance, ferrous chloride may be desired. The principles of operation of the, roaster are readily apparent, in that the ore particles being in very finely divided condition, burn autogenously as they fall through the oxidizing atmosphere, and the heat'thus generated aids in keeping the apparatus at a proper temperature depending, of course, upon the rates of flow of air and ore. It is desirable that the roasting operation be carried on at as low a temperature as is feasible for an autogenous roasting operation, and particularly if the ore material tends to sinter readily. It is, however,

. to be noted that the air separation of the ore particles, and the presence of lime, if used, will oppose the tendency for the ore to sinter.

The air introduced through the pipe 42 is con- .vertedto sulfur-oxygen gases which escape through the exit pipe 48, the air and gas flow being aided, if desired, by suitable 'fans or chimney construction. In order that the heat in this exit gas may be utilized in the drier, the gas is preferably passed through a heat exchange apparatus which is employed to heat the air forced into the drier chamber by means of the fan 25. Any suitable heat exchange apparatus may be employed, such as a standard rotary device in which the roaster gases and the cold air are alternately passed through a radiator-like structure arranged to revolve in such a manner that as the radiator webs become heated by the gases, they are immediately thereafter cooled by the incoming air. In the diagrammatic construction, the sulfur-oxygen gases pass through an annular chamber 49 and then outwardly through the pipe 50, while cold air is introduced through the pipe 5| into the inner chamber 52, from which it passes by means of, the pipe 53 to the fan 25 in its heated condition and at a proper temperature for the drier. It will be understood that the temperature of this gas may be suitably regulated by any standard and well-known means.

It will now be apparent that the invention in so far as. described comprises two cooperating units one a drier for, a wet but finely divided ore sludge or pulp, and the other a flash roaster for roasting this dried ore material, and which in turn provides sufiicient heat for the drying apparatus. This assembly of units may, therefore, be employed by itself and without reference to the other stages of the invention hereafter described. This invention is, however, particularly applicable to the chloridization of a sulfide ore since, by means of the apparatus above described, the ore has been put into a favorable condition for a subsequent process which is carried on with the ore in. a substantially dry condition. The ore in the flash roaster has not been allowed to sinter together or to formlarge aggregates, but remains as a finely divided powder; and in this condition, the ore material may be very easily and quickly treated with a chloridizing gas or with any other suitable gas, as is required, to solubilize the ore metal values. In accordance with this aspect of the invention, a complex sulfide ore containing the sulfides of zinc and iron together with various other metals, such as lead, silver, copper, etc., or a copper ore containing the various metals normally associated therewith, may be wasted in accordance with the above described steps and thus be suitably prepared for a subsequent solubilizing operation. It will be appreciated that a zinc ore may be roasted to either the oxide or ried on in accordance with the Mitchell process,

such as is described in the patents to Mitchell Nos. 1,943,332, 1,943,333, 1,943,335 of January 16, 1934, and 1,979,281 of November 6, 1934. Other standard chloridizing or solubilizing processes may, however, be employed.

A detailed description of the chloridization process will be found in said Mitchell patents, but in general it comprises the treatment of the oxidized ore material first in a warm absorber where it is subjected in a substantially dry condition to the weak chloridizing gases derived from later stages of the process or to hydrochloric acid and/or chlorine from any suitable source. This serves first to convert the zinc oxide to zinc chloride and then the iron oxide to iron chloride. If the iron oxide is in the ferric condition, this forms ferric chloride, but it is feasible to utilize ferrous oxide and to form ferrous chloride for the final finisher stage of the process. The chloridization of the two oxides, zinc and iron, is preferably carried on in two separate stages, as indicated in Figure 2, in which the zinc oxide is chloridized in a warm absorber at that temperature which is best adapted for its chloridization. .Also, the gases are passed through this absorber at such a rate relative to the temperature that the water of reaction is carried away sumciently fast to insure that the ore material remains in a subtantially dry and granular condition, as is fully set forth in the prior Mitchell patents. The temperature in this warm absorber may be from 80 C. to 110 C. or any other suitable temperature, as required for the purpose. The ore material is then passed to a secon cooled absorber which is preferably kept at a temperature below 90 C., and the ore material is there subjected to strong hydrochloric acid gas in the absence of any material amount of air. If

the quantity of air present is strictly limited to a small amount, then the temperature may be allowed to go to a much higher point without decomposition of the ferric and ferrous chlorides. Thereafter, the 'ore material is passed to the finisher, in which it is heat-ed to a temperature of 250 or 300 C. or higher, while air is passed in a counterflow relation over the ore material. The air reacts at this high temperature with the iron chlorides, and being in excess serves to convert them to ferric oxide and releases the chlorine thereof as nascent chlorine, but some hydrochloric acid may be formed, depending upon the amount of moisture present. The ore material is thus ultimately chloridized by means of these chloridizing gases. Further particulars of this procedure may be found in the prior Mitchell disclosure. 9

It will now be apparent that by means of this process, a complex sulfide ore or any other suitable ore material may be brought into a satisfactory condition for a subsequent chloridizing operation, and particularly because the flash roaster leaves it in a pulverulent condition and not sintered together into aggregates or a glassylike product, as is common in roasting processes. Also, the flash roasting operation is greatly aided by the-spray drying of the wet ore material, since the latter step leaves the material in a finely divided condition for efiicient roasting; The'wet particles being in free suspension cannot agglom crate during drying, and this dried pulverulent material is fed directly to the roaster without opportunity to form lumps or aggregations of particles. It will also be appreciated that the spray drying and the flash roasting steps serve both individually and collectively to prepare the ore material for the subsequent solubilizing treatments, in which it is required that the masame chamber, whereby the wet sludge first dries to a powder and the latter then becomes heated in the presence of air sufliciently to burn and give off its sulfur as a sulfur-oxygen gas. Various other modifications of the process are within the scope of this invention.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is: 1

1. The method of treating a raw sulfide ore comprising the steps of concentrating the ore in a finely divided condition by water flotation,

spraying the concentrated pulp of ore and water directly into a heated gas and thereby producing a substantially dry, pulverulent ore material, showering the ore powder into a heated atmosphere and fiash roasting an ore metal sulfide therein while maintaining the material in a pulverulent non-sintered condition, separating the roasted ore from the combustion gases and treating the pulverulent material in a substantially dry condition with a solubilizing gaseous re-,

agent and recovering an ore metal value therein.

2. The method of claim 1 in which the solubilizing action comprises subjecting the roasted ore in a substantially dry condition to the action of a chloridizing gas.

3. The method of roasting a sulfide ore comprising the steps of intermixing the ore in finely divided condition with water and an alkaline earth metal compound capable of aiding the roasting operation, spraying the wet mixture into a heated gas and removing the water therefrom while it is in suspension and thus providing a dry pulverulent ore material intimately associated with the alkaline earth metal compound, roasting this dry material with air and removing sulfide sulfur therefrom, while maintaining the mass in a non-sintered pulverulent condition and then treating the pulverulent material with a solubilizing reagent and recovering an ore metal value.

4. The method of roasting a sulfide ore comprising the steps of intermixing an alkaline earth metal compound and water with the ore material in finely divided condition, spraying the mixture into a heated atmosphere and removing the water therefrom and thus providing ore particles coated with the alkaline earth material, and thereafter showering the ore material into a heated roasting chamber while supplying air and maintaining a temperature sufficiently high to. cause the sul fide sulfur to burn, and removing the roaster gases and separating the dried ore powder therefrom.

' 5. The method of treating a sulfide ore comprising the steps of mixing the ore with an alkaline earth metal oxide and water and providing a finely divided intimate mixture thereof, then spraying the mixture into a heated atmosphere and evaporating the water therefrom and thus I providing finely divided ore particles coated and intimately mixed with the alkaline earth material, then flash roasting the material with sufii cient oxygen and at a temperature required to burn the sulfide sulfur and providing finely divided particles of roasted ore material, and thereafter treating the roasted'material with an agent capable of solubilizing an oxidized ore metal value.

6. The method of recovering values from a wet, finely divided sulfide ore comprising: the steps of spray drying the ore by contact with a heated gas while suspended therein and providing a substantially' dry, pulverulent ore, thereafter fiash roasting the ore while suspended in a heated oxidizing atmosphere and causing the removal of sulfide sulfur therefrom and thus providing an oxidized ore material, and subsequently subjecting 'the dry pulverulent roasted material to the action of a gas which readily permeates the material and solubilizes an ore value therein.

7. The method of treating a sulfide ore comprising the steps of grinding the ore material and providing a mixture thereof with water as a finely divided sludge, spraying the sludge into a closed chamber while passing a current of hot air therethrough and evaporating and removing the water therefrom, thereby providing a substantially dry, finely divided ore material, then showering said ore material into a large space and subjecting it while in suspension to the influence of air and sufficient heat to cause the sulfide sulfur thereof consisting of hydrochloric acid and chlorine under final temperature and oxidizing conditions which serve to convert'any iron chloride present to a chloridizing gas and ferric oxide and leave the desired ore metal values as chlorides.

THOMAS A. MITCHELL. 

